Post war, many urban centers in the US experienced white flight, it seems rational to assume that since these folks moved away from the cities to get away from minorities they would be against infrastructure that would allow minorities to "follow them" to the burbs. But these workers needed a way to get to the city for work, leisure, etc.
What better way to circle that square by building massive infrastructure which requires a middle class income (which allows you to buy a car) to use?
Even now we see lots of resistance by suburban communities to public transportation. In the Portland, OR metro area there is a upper middle class community called Lake Oswego, the residents have continuously lobbied against any form of public transportation in the town, lots of folks complaining about the "crime train".
The metro transit authority which designs new lines has succumbed to the pressure and the newly proposed line while in the vicinity of Lake Oswego avoids the town completely.